South Africa’s Drop in Covid-19 Cases Adds to Questions About Waves of Infections

 JOHANNESBURG—Earlier this year, doctors and epidemiologists in South Africa’s economic capital were bracing for the worst. a replacement coronavirus strain was surging across the country, thousands of holidaymakers were thanks to returning from Covid-19 hot spots, and one in three coronavirus tests was returning positive.

Then something unexpected happened: Covid-19 cases started dropping.

Since mid-January, confirmed Covid-19 infections in South Africa have fallen from a record of nearly 22,000 each day to around 1,000, without a large-scale vaccination campaign or stringent lockdown. Fewer than 5% of Covid-19 tests are finding traces of the virus, a symbol that health agencies are missing fewer cases. the govt has lifted most of its remaining virus restrictions for the country of 60 million people.

The explanation for this steep decline in cases remains somewhat of a mystery. As in other countries that have at some point experienced surprising drops in Covid-19 cases—such as India, Pakistan, and a few parts of Brazil—epidemiologists and virologists are piecing together different explanations for why the outbreak in South Africa isn’t following patterns set elsewhere.

Those range from important population groups reaching sufficient levels of immunity to hamper transmission, to people sticking more closely to social-distancing rules, like wearing masks and voluntarily reducing contacts when deaths were mounting before the decline.

“Anybody who professes certainty [about why infections started dropping] is lying,” said Harry Moultrie, a senior medical epidemiologist at South Africa’s National Institute for Communicable Diseases, or NICD. “There is such a lot uncertainty altogether of this.”

remains much scientists don’t realize how the coronavirus moves through society, often creating waves of infections whose peaks coincide with overwhelmed hospitals and enormous numbers of deaths. During the troughs, meanwhile, life in some places can feel almost normal again.

Filling the gaps within the world’s understanding of the virus could have important implications for public-health decisions. These include the way to calibrate government interventions like lockdowns, where best to focus on vaccines, and when a rustic or region has reached herd immunity—or if that's even possible, given the emergence of the latest coronavirus strains.

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One complicating thing about South Africa, as in another country, is that researchers don’t know the true toll of the virus on the population. due to limited testing capacities and asymptomatic infections, there are no definitive data on what percentage of people have recovered from Covid-19 and should now be immune.

Virologists are continuing to review the coronavirus variant, referred to as B. 1.351, that powered the newest wave of infections here. The strain appears to form some existing vaccines less effective and, in some cases, has reinfected people that had recovered from a previous bout of Covid-19.

In contrast to the slump in cases, much of Europe experienced last summer, the present drop by infections in South Africa didn’t follow a strict government-imposed lockdown. At the turn of the year, which overlaps with the Southern Hemisphere’s main summer vacation, the govt closed popular beaches, tightened the nightly curfew, and banned large social gatherings and therefore the sale of alcohol. A national mask mandate has been in situ since April 2020.

Indoor dining at limited capacity, however, was permitted throughout and lots of families came together for Christmas and New Year’s. Most restrictions came only after tens of thousands of South Africans working in economic centers like Johannesburg had already traveled to ascertain family in provinces where Covid-19 case numbers were double the records set in July, during the primary wave. Workers’ return range in early January, often piled into shared minibus taxis that are a standard means of conveyance in South Africa, created perfect conditions for the virus to spread.

The simplest explanation for the sudden mid-January drop by cases is that sections of the population had reached A level of immunity that made it harder for the virus to leap between different groups, said Jinal Bhiman, a principal scientist at the NICD.

Only about 1.5 million South Africans, around 2.5% of the population, have tested positive for Covid-19. But the particular level of infection has been much higher. Since cases first started surging in May, the country has recorded quite 145,000 excess deaths, of which 85% to 95% are likely thanks to Covid-19, consistent with the South African Medical Research Centre. meaning that about one in 500 people in South Africa—where the median age maybe a decade below the U.S.—has died of the disease over the past 10 months.

South African researchers, after testing the blood of 4,858 donors for antibodies in January, estimated that within the two hardest-hit provinces quite half of the people between the ages of 15 and 69 had already had Covid-19. But it's unlikely that immunity levels are equally high in other parts of the country.

Experts even have warned that blood donors aren’t representative of the general population, as shown by the recent resurgence of infections within the Brazilian city of Manaus, where an antibody study of donated blood last year found similar results.

In the absence of national herd-immunity, scientists specialize in the role of certain networks, or individuals with many social or work contacts, in driving and eventually slowing down localized outbreaks. “Highly sociable people get infected first, and therefore the virus moves through these networks,” said Dr. Moultrie. When enough people in those networks became immune, transmission peters out.

Researchers around the world also are studying the impact of voluntary changes in behavior, which may anticipate and strengthen government-imposed restrictions. “When the rates go up, people modify their behavior,” said Saad Omer, director of the Yale Institute for Global Health. even as a little increase in social contacts can drive an exponential rise in infections, curtailing gatherings when infections are already declining can further hasten the autumn.

“Small changes can have massive consequences,” Dr. Omer said.

Perhaps the foremost difficult question to answer is what's getting to happen next. Will cases go up again, perhaps powered by yet one more coronavirus strain, as happened about two months after South Africa ended its first wave of infections in September? Juliet Pulliam, who directs South Africa’s Centre of Excellence in Epidemiological Modeling and Analysis, says there are no thanks to knowing.

“I don’t think it's possible to predict with certainty when, or maybe whether, there'll be a 3rd wave in South Africa,” she said.

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